Widgetsnbextension: throw error on failure to render

[martinRenou]

This goes in pair with jupyter/notebook#6181

[github-actions]

👈 Launch a binder notebook on branch martinRenou/ipywidgets/throw_error_on_failure_to_render

[SylvainCorlay]

+1 on this.

This will enable viewing alternative mime types when widgets cannot be rendered. It would be interesting to have a independent release of widgetsnbextension with that change.

[martinRenou]

TODO

• What happens for current Notebook?
• Should we do a Notebook version check?

[martinRenou]

Now doing a Notebook version check to not change the behavior for Notebook 6.4.4 and before.

[SylvainCorlay]

Discussed during the ipywidgets call. Merging as decided in the call.

[SylvainCorlay]

@meeseeksdev backport to 7.x

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

$ git checkout 7.x
$ git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

$ git cherry-pick -m1 3558ce6a22b4a6b1badb69f0507a6ac5b245a17f

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

$ git commit -am 'Backport PR #3280: Widgetsnbextension: throw error on failure to render'

4. Push to a named branch :

git push YOURFORK 7.x:auto-backport-of-pr-3280-on-7.x

5. Create a PR against branch 7.x, I would have named this PR:

"Backport PR #3280 on branch 7.x (Widgetsnbextension: throw error on failure to render)"

And apply the correct labels and milestones.

Congratulation you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove Still Needs Manual Backport label once the PR gets merged.

If these instruction are inaccurate, feel free to suggest an improvement.

[jasongrout]

Backported to 7.x in #3290